When a statistical model is constructed, and variables are correlative to each other in a regression model, a stable model may not be constructed, which is referred to as multicollinearity. Stratification of data is considered as a scheme of solving multicollinearity.
When stratification is minutely performed, accuracy is improved, and multicollinearity can be solved. However, there are problems that the number of included samples decreases, and a reliable statistical model cannot be constructed.